From acf9482c1d19f5d6dc2f7261e73e45ccc8becffd Mon Sep 17 00:00:00 2001
From: Gordon Williams <gw@pur3.co.uk>
Date: Thu, 5 Dec 2024 10:08:54 +0000
Subject: [PATCH] Ensure STM32_I2S_AddSamples starts playback if there isn't
 enough space, fix issue where calling AddSamples with too big a buffer would
 always cause failure

---
 libs/pipboy/stm32_i2s.c | 28 +++++++++++++++++++++++-----
 libs/pipboy/stm32_i2s.h |  6 ++++++
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/libs/pipboy/stm32_i2s.c b/libs/pipboy/stm32_i2s.c
index 90c0d906f..b2fc17ec6 100644
--- a/libs/pipboy/stm32_i2s.c
+++ b/libs/pipboy/stm32_i2s.c
@@ -244,10 +244,13 @@ int STM32_I2S_GetFreeSamples() {
 
 // Add samples to the ringbuffer
 void STM32_I2S_AddSamples(int16_t *data, unsigned int count) {
-  int timeout = 1000000;
-  while ((STM32_I2S_GetFreeSamples() < (int)count+32) && --timeout); // wait here for space
-
+  // Try and fill until ringbuffer is full
+  unsigned int freeSamples = STM32_I2S_GetFreeSamples();
   unsigned int c = count;
+  if (c > freeSamples) {
+    c = freeSamples;
+    count -= freeSamples;
+  } else count = 0;
   while (c--) {
     audioRingBuf[audioRingIdxIn] = *(data++)
                                  + (audioRingIdxIn&1); // add 1 bit of noise to stop DAC from turning off!
@@ -255,8 +258,8 @@ void STM32_I2S_AddSamples(int16_t *data, unsigned int count) {
   }
 
   //jsiConsolePrintf("add %d %d %d %d\n", i2sDMAidx, i2sStatus, count, audioRingBufGetSamples());
-  // start playback when we have enough
-  if (i2sStatus == STM32_I2S_STOPPED && audioRingBufGetSamples()>I2S_DMA_BUFFER_SIZE*3) {
+  // start playback if we have enough
+  if (i2sStatus == STM32_I2S_STOPPED && audioRingBufGetSamples()>=I2S_DMA_BUFFER_SIZE*3) {
     // if audioRingBufGetSamples()>I2S_DMA_BUFFER_SIZE*3 we should have enough here to fill 6 buffers
     i2sDMAidx = !DMA_GetCurrentMemoryTarget(DMA1_Stream4);
     fillDMAFromRingBuffer(); // fill the first buffer with what we're currently reading from!
@@ -264,6 +267,21 @@ void STM32_I2S_AddSamples(int16_t *data, unsigned int count) {
     fillDMAFromRingBuffer(); // fill the second buffer
     STM32_I2S_Start();
   }
+
+  if (!count) return;
+  // otherwise we still have more to put in - try and wait a bit
+  if (STM32_I2S_GetFreeSamples() < (int)count) {
+    // wait until we have space
+    int timeout = 1000000;
+    while ((STM32_I2S_GetFreeSamples() < (int)count) && --timeout); // wait here for space
+  }
+  // now attempt to put in the rest but drop any we don't have space for
+  c = count;
+  while (c-- && STM32_I2S_GetFreeSamples()) {
+    audioRingBuf[audioRingIdxIn] = *(data++)
+                                 + (audioRingIdxIn&1); // add 1 bit of noise to stop DAC from turning off!
+    audioRingIdxIn = (audioRingIdxIn+1) & (I2S_RING_BUFFER_SIZE-1);
+  }
 }
 
 void STM32_I2S_Start() {
diff --git a/libs/pipboy/stm32_i2s.h b/libs/pipboy/stm32_i2s.h
index d26319c67..a26330e6f 100644
--- a/libs/pipboy/stm32_i2s.h
+++ b/libs/pipboy/stm32_i2s.h
@@ -22,6 +22,12 @@
 #define I2S_RING_BUFFER_SIZE 8192 // size of ringbuffer used for audio input in u16
 // 8192 seems fine to use - still enough for 8 DMA packets worth/0.5sec...
 
+/* jswrap_pb_audioFrame sends data in 2048 byte chunks and STM32_I2S_AddSamples
+starts playback at 3*I2S_DMA_BUFFER_SIZE. So I2S_RING_BUFFER_SIZE=8192
+is the least we can use, since any less and 3*I2S_DMA_BUFFER_SIZE would be
+big enough that the next sample from jswrap_pb_audioFrame would fill the buffer */
+
+
 typedef enum {
   STM32_I2S_STOPPED,
   STM32_I2S_PLAYING